This invention relates to impregnated granules. In particular, this invention relates to porous granules containing liquid material held therein for controlled release by a polyurethane matrix.
The invention further relates to a process for preparing such impregnated granules. The effect of the impregnation is to control the rate of release of a liquid material, e.g. a liquid pesticide material to the surrounding environment where applied. The impregnation thus serves to increase the effectiveness and the useful life of the liquid contained in the treated granules. By limiting the maximum rate of diffusion of the liquid material from the pores, the polyurethane matrix helps to prevent the usual occurrence of a rapid and excessive initial release.
The use of membranes, coating, and capsules for the controlled release of liquid materials is well known in the art of both agricultural and non-agricultural chemicals. In the agricultural area, such controlled release techniques have improved the efficiency of herbicides, insecticides, fungicides, bactericides, and fertilizers, coating technology for agricultural uses include coated droplets, such as microcapsules, coated solids such as porous or non-porous particles, and coated aggregates of solid particles. Non-agricultural uses include encapsulated dyes, inks, pharmaceuticals, flavoring agents, and fragrances.
Many prior art coatings completely enclose the material held inside, and prevent any release of the material until the coating is broken, dissolved, or otherwise removed. There is a need in the agricultural industry for a granular product containing a pesticide material that allows the controlled release of the entrapped pesticide material to the surrounding medium.
Porous granules of this invention offer distinct advantages for the application of chemicals in a wide variety of commercial applications by improving the ease of handling as well as the ease of distributing or dispersing the chemicals over a wide area, and by offering controlled release characteristics. In addition, porous granules of high pore volume are capable of retaining a considerable volume of liquid inside their pore structure, with only a small fraction of liquid initially exposed to the outer surroundings.
It is therefore an object of this invention to provide a process for the preparation of porous granules impregnated with a liquid material and to provide for a polyurethane matrix which permits the uniform distribution of the liquid material inside the porous structure of the granules and provides for a controlled rate of release of the liquid material.
Another object of this invention is to provide a novel composition of matter of an impregnated granule with the pore structure uniformly filled with a polyurethane polymer that is capable of providing a controlled rate of release of the liquid contained in the structure of the polyurethane material.